netdev - Re: [PATCH bpf-next v2 1/6] xsk: add tracepoints for packet drops

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Date:   Thu, 28 Jan 2021 00:15:34 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     "Loftus, Ciara" <ciara.loftus@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        "bjorn@...nel.org" <bjorn@...nel.org>,
        "Janjua, Weqaar A" <weqaar.a.janjua@...el.com>
Subject: Re: [PATCH bpf-next v2 1/6] xsk: add tracepoints for packet drops

On 1/27/21 3:10 PM, Loftus, Ciara wrote:
[...]
> 
> Thanks for your feedback Daniel.
> 
> The stats tell us that there is *a* problem whereas the traces will shed
> light on what that problem is. eg. The XSK_TRACE_DROP_PKT_TOO_BIG
> trace tells us we dropped a packet on RX due to it being too big vs. ss
> would just tell us the packet was dropped.

But wouldn't that just be a matter of extending struct xdp_diag_stats +
xsk_diag_put_stats() with more fine-grained counters? Just wondering given
you add the trace_xsk_packet_drop() tracepoints at locations where we
bump most of these counters already for ss tool. I guess this was my confusion -
as far as I can see only the two XSK_TRACE_DROP_{PKT_TOO_BIG,DRV_ERR_TX} are
not covered in xdp_diag_stats. Is there any other reason that the diag is
not sufficient for your use case?

Thanks,
Daniel